Various devices have been designed in the past to provide means of partially or fully decoupling and coupling the vibration damping characteristics of hydraulic mounts for engines for motor vehicles in response to changes in driving and engine operating characteristics. Because damping forces add to spring forces to create a high dynamic rate (force/deflection); it is desirable to eliminate the damping when it is not needed. Therefore, most hydro-elastic mount designs include devices that de-activate or "decouple" the damping for relatively small amplitude flexing.
A typical engine mount contains two sealed chambers separated by an intermediate partition having a damping channel passing therethrough and providing communication between the chambers. The engine mount normally has one end member attached to an engine block and another end member attached to a vehicle frame, with the end members being resiliently connected to each other by an elastomeric member which permits one end member to move in response to vibrations with respect to the other. In order to damp vibrations between the two end members, hydraulic fluid is pumped back and forth from one chamber to the other through the damping channel in the partition. In order decouple the damping action, it is necessary to prevent the hydraulic fluid from flowing back and forth through the channel by providing another alternative response to vibrations which would normally tend to pump the hydraulic fluid through the damping channel.
One type of device for adjusting damping in an engine mount is the use of an inflatable bladder mounted inside the primary fluid chamber as shown in U.S. Pat. Nos. 4,840,358 and 4,901,986.
Another approach to the problem is shown in U.S. Pat. No. 4,886,251 in which an inflatable diaphragm inside the pressure chamber forms an air chamber with the end member and an elastomeric spring member. When air pressure is inserted into the air chamber, the diaphragm is lifted off the spring member and bears against the annular partition wall and prevents any vibration from being transmitted from the elastomeric spring member to the damping fluid in the pressure chamber. This causes decoupling of any damping which would otherwise occur if the air chamber were not inflated.
U.S. Pat. No. 4,886,252 shows decoupling of the damping action of the engine mount by changing the wall area or volume of the damping channel.
U.S. Pat. No. 4,712,777 shows another decoupling device which uses an air chamber covered by a diaphragm adjacent to the fluid pressure chamber of the engine mount. The diaphragm contains a shutter panel which can be closed to isolate the diaphragm from the pressure chamber. When the diaphragm is isolated from the pressure chamber, fluid is pumped through the damping channel by vibration imparted to the fluid. When the shutter panel lifts off a seated position and exposes the diaphragm to communication with the pressure chamber, then deflection of the diaphragm will occur in response to vibrations imparted to the fluid, and such deflection will result in either partial or complete decoupling of the damping action by reducing or preventing fluid from flowing through the damping channel. The present invention is intended to provide certain advantages over the prior art decoupling devices as will be described in the following specification.